This invention relates to athletic shoes, and more particularly this invention relates to a sole construction for athletic shoes.
Nowadays, there is a great emphasis on improving the health and physical well being of men and women alike by indulging in a regular program of exercise. Particular emphasis is placed on running or jogging as a means of exercise which stimulates the heart, improves the respiratory system, and tones a variety of muscles. With this emphasis on running and jogging, however, there is an equally important emphasis on the proper footwear to provide both comfort and protection against injury.
Athletic shoes used primarily for running or jogging have undergone a number of evolutionary changes in their design. Much development has gone into the design of the uppers of the shoes which have reached a stage of development wherein improvements are minor. Current emphasis is placed on weight, flexibility, and sock absorbency of the shoe. These considerations are primarily functions of sole design. There are a great many styles and types of such athletic shoes presently being marketed, most of them providing good foot support and clearly serving the purpose for which they are sold. But, all of them suffer from a common disadvantage, namely, they sacrifice light weight for shock absorbency, or vice versa. Some designs, while attempting to solve the problems inherent in a running shoe, either exacerbate the problems or solve them in a complex manner which adds to the cost of manufacture and, naturally, to the cost of the shoe.
For instance, in U.S. Pat. No. 4,030,213, a construction is disclosed which utilizes a rigid sole extending the full length of the shoe and curving upwardly at the heel end and the toe end to be joined to the upper. The rigid sole member could be made of hard rubber or of metal and is convex to provide a "pedestal" beneath the wearer's arch. A pair of resilent sole members are applied over the rigid sole at the heel end and at the toe end, these resilient members also being convex. The net effect when the wearer takes a step is to provide a double rocking motion. Furthermore, in one embodiment, a number of springs are embedded in the various sole members to provide additional resiliency.
In U.S. Pat. No. 4,128,950, there is disclosed an athletic shoe which is somewhat lighter in weight than other prior art shoes utilizing, intermediate the upper and the outer sole, a heel lift sole layer of resilient lightweight synthetic plastic foam cushioning material and extending under the heel and the arch of the wearer, and an intermediate sole layer of a similar plastic foam material extending the full longitudinal length of the shoe. Both the heel lift sole layer and the intermediate sole layer are made of the same foam material which is preferably a polyethylene having a hardness, A-type, durometer, 68.degree. F. of 35-37, or a polyethylene vinyl acetate having a hardness of 26-29. Because the material of which these layers is made is quite soft, it is necessary to further include a lateral stabilizer plate between the two layers and situated under the wearer's heel. In an alternative embodiment, the heel lift layer (to be distinguished from the heel lift sole layer) has an outer border portion made of a hard crepe rubber surrounding a relatively soft core portion made of a soft foam. The use of the soft core portion is for the purpose of stabilizing the shoe and the use of the crepe rubber outer portion is for the purpose of providing greater lateral stability.
The disadvantage of this prior art shoe lies in the use of an extremely soft foam which renders the shoe inherently unstable and thereby necessitates the use of a rigid stabilizer plate or a crepe rubber border in the heel and arch area of the shoe thereby adding to the weight and having all the undesirable characteristics of other prior art shoes.